Identifier discrimination: realizing selective-ID HIBE with authorized delegation and dedicated encryption privacy

It has been almost one and a half decades since the introduction of the concept of hierarchical identity-based encryption (HIBE) systems, and many pairing-based HIBE systems have been proposed; however, how to achieve independent private key delegation in HIBE systems is still open. Independent private key delegation in HIBE systems requires that the following three conditions are satisfied: (1) private keys are not valid delegation credentials for deriving descendants’ private keys, (2) any entity intending to derive a private key for any one of its descendants should own a valid delegation credential distributed by the root private key generator (PKG), and (3) a credential is only valid for deriving private keys for a given descendant. We present a new technique for composing private keys for entities in HIBE systems that we call identifier discrimination, aiming at resolving the problem of independent private key delegation. With the technique, we construct a selective identity secure HIBE system under the decisional bilinear Diffie–Hellman (DBDH) assumption in the standard model with the following properties. (1) Every entity in the HIBE system is prevented from deriving private keys for its descendants with the only use of its private key and the public parameters. (2) The root PKG can delegate the privilege (if needed) of generating private keys for each individual entity to any of its ancestors through authorization that we call authorized delegation, by distributing a specifically crafted secret (delegation credential) to the ancestor. (3) The encryption privacy of each ciphertext for its intended recipient is achieved, that is, ciphertexts encrypted on identity of any entity cannot be decrypted by any of its ancestors that we call dedicated encryption privacy.